This invention relates to a method and apparatus for removing volatile contaminants from contaminated soil, and more particularly, to a method and apparatus for removing volatile contaminants from contaminated soil which involves vapor tight containment of the contaminated soil and volatilization of the organic contaminants ("VOCs") by inducing air flow through the containment system.
Contamination of soils is an ever-increasing problem in today's society. Contamination has typically been caused as a result of spills, dumping of hazardous liquids, leakage from underground storage tanks, etc., where the contaminants are retained by the subsurface soil. An immediate health threat is posed when these contaminants descend hydrodynamically into the groundwater. Additionally, the balance of the ecosystem is severely disturbed as surrounding plant and animal life is directly affected by the contaminated soil. It is thus desirable to develop a method and apparatus to remove the volatile contaminants from the contaminated soil.
Often, excavation of the soil is required to immediately remove and reduce the source of contamination at a site where a discharge of volatile organic contaminants has occurred. Excavation is typically required when immediate removal and management of the contaminated soil is either required by federal, state or municipal regulations or is determined to be required as an immediate response effort to reduce the source of the contamination. Examples of situations where excavation of the soil is often implemented include underground storage tank removals, emergency responses to accidental spills of hazardous materials, and excavation of uncontrolled hazardous material disposal sites, etc.
The primary method of management of contaminated soil resulting from underground storage tank and source removals has been and is presently off-site disposal at a landfill. This is the most expensive remedial option for management of contaminated soils and creates additional liability for the generator because the disposal site could most likely become a future uncontrolled hazardous waste site and require the disposed materials to be remanaged. On-site treatment methods for excavated soils include thermally enhanced vaporization, which requires heating and rotating of contaminated soils in a cylindrical container, such as is described in U.S. Pat. No. 4,748,921, and solvent stripping, which requires separation of the solids in the soil and leaching of contaminants from the solids with a leaching solvent, such as is described in U.S. Pat. Nos. 4,801,384 and 4,869,825. In these prior on-site treatment methods for excavated soils, process flow volumes are limited due to design constraints and substantial capital is required for initial development and construction of the technology.
Several methods for removing VOCs from contaminated soils in situ are known and described. The primary drawback for application of in situ technology is that the extent and occurrence of contamination in the subsurface must be adequately defined via field exploration methods prior to implementation. Additionally, field investigation results may indicate site limiting conditions which would prohibit application of in situ technology. Site limiting conditions for application of in situ technology include: shallow depth to bedrock, irregular bedrock topography, shallow depth to water table, heterogeneous subsurface materials such as fill, and confining subsurface strata.
In situ methods for removing VOCs are described in U.S. Pat. Nos. 4,834,194; 4,850,745; 4,849,360; 4,745,850; 4,593,760; 4,730,672; and 4,842,448. U.S. Pat. No. 4,834,194 describes a method in which an apparatus protrudes into, agitates, and heats a subsurface volume of soil. U.S. Pat. Nos. 4,849,360 and 4,850,745 disclose methods for treating soils contaminated with organic compounds and petroleum hydrocarbons, respectively, which involve aerobic biodegradation of contaminants. Both methods require a population of microorganisms capable of degrading the specific contaminants to be effective. In situations where the soils are extremely contaminated, conditions within the soil matrix are often found to be toxic to these microorganisms, and therefore, these methods are not effective for all applications. U.S. Pat. Nos. 4,745,850; 4,593,760; 4,730,672 and 4,842,448 describe methods for removing volatile organic VOCs from contaminated soil in situ using vapor extraction methods.